1. Field of the Invention
The present invention relates to a method for preparing microtubular halloysite nanopowders and, more particularly, to a method for preparing microtubular halloysite nanopowders by cutting halloysite nanotubes at a high pressure, microtubular halloysite nanopowders prepared by the method, and a cosmetic composition comprising the microtubular halloysite nanopowders.
2. Description of the Related Art
Halloysite, a kind of natural clay mineral, is an aluminosilicate mineral with a 1:1 layer structure consisting of a tetrahedral silica layer, an octahedral alumina layer, and a layer of water molecules situated between the two layers. Most halloysites are natural minerals in the form of long tubes having an aspect ratio of 10 or more and are called “nanotubes” as they have an inner diameter of about 10 to 15 nm.
Halloysite nanopowders can be used as a container or carrier of nano sized particles or organic materials such as drugs, cosmetics, etc. Moreover, the halloysite nanopowders are environmentally-friendly nanomaterials that can maintain the efficacy for a long time, and thus the halloysite nanopowders can be used as high value-added materials in many industrial fields.
However, the natural halloysite has a long tube-like shape, and thus if it is injected into a blood vessel, it may damage cells. Moreover, if it is used as a cosmetic, it causes irritation to the skin or it makes it difficult to achieve a soft feel. To solve these problems, a technique for preparing halloysite nanopowders having a length of several micrometers with a tubular shape that can contain the contents is required.
Meanwhile, the halloysite has a diameter of 30 to 250 nm and a length of 0.2 to 40 μm, and thus it is difficult to separate the nanoparticles using conventional mineral separation techniques. For example, the sieving can be done up to several microns, and an effective filtration for solid-liquid separation cannot be effectively used for solid-solid separation. While commercially available apparatuses using a cyclone principle can effectively separate powders of 1 μm or less from powders having a particle size greater than 1 μm, it is not known whether they can be used to separate rod-like powders, and further it is difficult to separate submicron-sized powders.
In addition, there are many conventional techniques for separating nanoparticles ranging from several tens of microns to submicron size, such as field-flow fractionation (FFF), hydrodynamic chromatography (HDC), capillary hydrodynamic fractionation (CHDF), split-flow thin (SPLITT) fractionation, and pinched flow fractionation (PFF). However, these conventional techniques are aimed at separating blood components, and there are many problems that a complicated external device for particle injection is required, and it takes a lot of time to ensure accurate separation. Therefore, a technique for separating and selecting mineral powders in large quantities is required.
Recently, there is extensive research that pays attention to carbon nanotubes serving as a carrier for microparticles and aims at using the carbon nanotubes. However, a method for effectively cutting natural halloysite to have a length of several micrometers with a tubular shape has not been reported so far.
Therefore, the inventors of the present invention have made extensive efforts to develop a method for ultra-fine grinding natural halloysite to a short length and selecting halloysite nanopowders having an appropriate size according to the application field and, as a result, have confirmed that it is possible to prepare a halloysite having a length of several micrometers and maintaining the tubular shape by using a method of cutting halloysite nanotubes at a high pressure and a method of selecting halloysite nanopowders using a continuous centrifuge, thereby completing the present invention.